1. Field of the Invention
The present invention relates to an active matrix substrate, pixel defect correcting method and its manufacturing method. More particularly, it relates to an active matrix substrate especially suitable for a component member of a liquid crystal display device having a pixel-divided (multi-pixel) structure, its pixel defect correcting method and manufacturing method, and a liquid crystal display device and its manufacturing method.
2. Background Art
An active matrix substrates is widely used in active matrix display devices such as a liquid crystal display device, a EL (Electro Luminescence) display device and the like. According to the active matrix substrate used in a conventional active matrix display device, a switching element such as a TFT (Thin Film Transistor) and the like is provided at each intersecting point between a plurality of scanning signal lines and a plurality of data signal lines arranged on the substrate so as to intersect with each other. An image signal is appropriately transferred to each pixel (electrode) part connected to the TFT and the like, by a switching function of the TFT and the like. In addition, in order to prevent deterioration of the image signal caused by a self-discharge of a liquid crystal layer or an off current of the TFT and the like while the TFT is off, or to be used in a path and the like to apply various kinds of modulation signals in liquid crystal driving, there is provided an active matrix substrate having a storage capacitor element in each pixel part.
As a constitution of the active matrix substrate used in the conventional active matrix liquid crystal display device, the following constitution is known (refer to Japanese Kokai Publication No. 09-152625 (PP. 1 and 19, FIG. 7), for example).
FIG. 23 is a schematic plan view showing one pixel of the active matrix substrate provided in the conventional active matrix liquid crystal display device.
As shown in FIG. 23, a plurality of pixel electrodes 51 are provided on the conventional active matrix substrate in the shape of a matrix. The scanning signal line 52 to supply a scanning line signal and the data signal line 53 to supply a data signal pass around the pixel electrode 51 and intersect with each other. In addition, as a switching element to be connected to the pixel electrode, the TFT 54 is provided at an intersecting part between the scanning signal line 52 and the data signal line 53. The scanning signal line 52 is connected to a gate electrode of the TFT 54 and the TFT 54 is driven and controlled when the scanning signal is inputted. In addition, the data signal line 53 is connected to a source electrode of the TFT 54 so that the data signal is inputted. Furthermore, the drain extraction wiring 55 is connected to a drain electrode of the TFT 54, one electrode 55a of the storage capacitor element (a storage capacitor upper electrode) is connected to the drain extraction wiring 55, and the pixel electrode 51 is connected to the storage capacitor upper electrode 55a through the contact hole 56. The storage capacitor (common) wiring 57 functions as the other electrode of the storage capacitor element (a storage capacitor lower electrode).
FIG. 24 is a schematic sectional view showing one pixel of the conventional active matrix substrate taken along line A-A′ shown in FIG. 23.
As shown in FIG. 24, the conventional active matrix substrate comprises the gate electrode 62 connected to the scanning signal line 52, and the storage capacitor (common) wiring 57 on the transparent insulation substrate 61 formed of glass, plastic and the like. The scanning signal line 52 and the gate electrode 62 are formed of a metal film such as titanium, chrome, aluminum, molybdenum and the like, their alloy film or their laminated film by sputtering and the like, and then patterned by photo-etching and the like. The storage capacitor (common) wiring 57 is formed of the same material as that of the scanning signal line 52 and the gate electrode 62.
In addition, the gate insulator 63 is provided so as to cover the gate electrode 62 and the storage capacitor (common) wiring 57. The gate insulator 63 comprises an insulation film such as a silicon nitride film, a silicon oxide film, a metal oxide film and the like. Thereon provided is the high-resistance semiconductor layer 64 formed of amorphous silicon, polysilicon and the like so as to overlap with the gate electrode 62, and thereon provided as an ohmic contact layer is a low resistance semiconductor layer formed of n+ amorphous silicon and the like doped with an impurity such as phosphorus which becomes the source electrode 66a and the drain electrode 66b. The insulation film, amorphous silicon, n+ amorphous silicon and the like are formed by plasma CVD (Chemical Vapor Deposition) and the like and patterned by photo-etching.
In addition, the data signal line 53 is provided so as to connect to the source electrode 66a. In addition, the drain extraction wiring 55 is provided so as to be connected to the drain electrode 66b. The drain extraction wiring 55 is elongated to constitute the storage capacitor upper electrode 55a which is the one electrode of the storage capacitor element and it is connected to the pixel electrode 51 through the contact hole 56. The data signal line 53, the drain extraction wiring 55 and the storage capacitor upper electrode 55a are formed of the same material and a metal film comprising titanium, chrome, aluminum, molybdenum and the like, their alloy film or their laminated film by sputtering and patterned by photo-etching. The pixel electrode 51 is formed of a transparent conductive film such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), tin oxide, zinc oxide and the like. The contact hole 56 is formed so as to penetrate the interlayer insulation film 68 formed so as to cover the TFT 54, the scanning signal line 52, the data signal line 53 and the drain extraction wiring 55. Examples of materials of the interlayer insulation film 68 include an acrylic resin, silicon nitride, silicon oxide and the like.
According to the active matrix substrate having the above constitution, in order to simplify its manufacturing process and reduce its manufacturing cost, the storage capacitor (common) wiring (the storage capacitor lower electrode) 57 is formed at the same step as that of the scanning signal line 53 and the storage capacitor upper electrode 55a is formed at the same step as that of the data signal line 53 and the drain extraction wiring 55.
Like the active matrix substrate shown in FIGS. 23 and 24, when the pixel electrode is formed on the interlayer insulation film, the pixel electrode may overlap with each signal line. And therefore a high aperture ratio may be obtained and an electric field from each signal line to the pixel electrode may be shielded. At this time, as shown in FIG. 23, by forming the contact hole 56 in the interlayer insulation film 68 to connect the pixel electrode 51 to the storage capacitor upper electrode 55a, the pixel electrode 51 and the drain electrode 66b are connected through the drain extraction electrode (wiring) 55. The position of the contact hole 56 is not necessarily formed above the storage capacitor upper electrode 55a and it may be formed above the drain extraction electrode (wiring) 55. And when it is formed above the storage capacitor upper electrode 55a positioned above the storage capacitor (common) wiring pattern 57 as shown in FIG. 23, the aperture ratio is not further reduced.
Recently, in a liquid crystal display device used in a large liquid crystal TV and the like, in order to increase viewing angle, a VA (Vertical Alignment) method having a multi-domain, that is, an MVA (multi-domain Vertical Alignment) method has been widely spread (refer to Japanese Kokai Publication No. 2002-122869 (PP. 2 and 21, FIG. 2), for example and Japanese Kokai Patent Publication No. 2001-83523 (PP. 1 and 55, FIG. 17), for example). According to the MVA method, the wide viewing angle is implemented by providing a removal pattern or a protrusion for controlling an alignment of a liquid crystal molecule in the pixel electrode of the active matrix substrate and an opposed electrode of an opposed substrate and using a formed fringe field to disperse the alignment direction of the liquid molecule to a plurality of directions. In addition, also in the conventional active matrix substrate shown in FIGS. 23 and 24, the wide viewing angle may be implemented by providing the removal pattern or the protrusion for controlling an alignment of the liquid crystal molecule in the pixel electrode of the active matrix substrate and the opposed electrode of the opposed substrate.
In addition, in order to prevent a light leakage and improve an initial response speed after application of a voltage, there is a technique in which an electrode is buried in a position corresponding to the removal pattern (referred to as an electrode slit also hereinafter) of the pixel electrode or the opposed electrode (refer to Japanese Kokai Patent Publication No. 10-333170 (PP. 1, 2, and 4) and Japanese Kokai Patent Publication No. 2001-117083 (PP. 1, 2, 4, 6, and 12, FIG. 21), for example).
In the manufacturing process of the active matrix substrate, a short circuit (leak) may generate between the source electrode and the drain electrode of the TFT, or the drain electrode or the drain extraction wiring is broken because of a foreign material, a film remaining and the like. In addition, an operation defect of the TFT may generate because the ohmic contact is insufficiently provided. Thus, a normal voltage (drain voltage) is not applied to the pixel electrode of the pixel in which the defect is generated, so that a point defect such as a luminance point or a black point is generated on a display screen in the liquid crystal display device, resulting in reduction of a manufacturing yield of the liquid crystal display device.
Regarding correction of such a pixel defect, a liquid crystal display panel or a liquid crystal display device having a structure in which an interconnection wiring for correction is previously provided between the pixel and the adjacent pixel has been disclosed (refer to Japanese Kokai Publication No. 59-101693 (P. 1), Japanese Kokai Publication No. 2-135320 (PP. 1 and 4, FIG. 1), Japanese Kokai Patent Publication No. 8-328035 (PP. 1 and 5, FIG. 1), and Japanese Kokai Patent Publication No. 2002-350901 (PP. 17 and 24, FIG. 20), for example). According to the above, when the pixel defect is generated, the pixel in which the pixel defect is generated may be driven by applying laser to the interconnection wiring for correction to electrically connect the pixel electrode of the pixel in which the pixel defect is generated to the pixel electrode of the adjacent pixel and applying a voltage of the same potential as that of the adjacent pixel.
However, there is room for improvement in this method in view of the following points. That is, the pixels are insulated in a normal state (at the time of normal operation) and it is necessary that the interconnection wiring for correction runs over the pixels. Therefore increase of an area of the interconnection wiring for correction may reduce the aperture ratio. In addition, even when the drain electrode or the drain extraction wiring is broken, the defect should be corrected in the own pixel since the TFT of the pixel in which the line is broken can normally operate. The reason is when the pixel in which the line is broken is driven through the interconnection wiring for correction, an extra driving load is applied to the TFT of the adjacent pixel. Meanwhile, according to the above method for correcting the pixel defect, the correction can be made only by connecting the adjacent pixels and the correction cannot be made in the own pixel.
In addition, regarding a method for solving a TFT defect, disclosed is a structure of a liquid crystal display device having a redundant structure in which a plurality of TFTs are connected in parallel in one pixel. (refer to Japanese Kokai Publication No. 07-199221 (PP. 1 and 6, FIG. 1), for example). However, according to this structure of the liquid crystal display device, there is room for improvement because the pixel defect cannot be corrected when all TFTs in the pixel become defective.
In addition, regarding a method for restoring the point defect of the transparent pixel electrode because of the defect of the TFT, disclosed is a constitution of a liquid crystal display device comprising a redundant circuit other than the switching element which can connect at least one of the scanning line (scanning signal line) and the signal line (data signal line) to the pixel electrode (refer to Japanese Kokai Publication No. 11-282007(PP. 1 and 2), for example). However, according to this constitution of the liquid crystal display device, since the signal line and the transparent pixel electrode are the same potential, the luminance point or a decalescence point of the transparent pixel electrode can be a semi-luminescence point, but the pixel defect cannot be perfectly corrected.